Invisible tear seam for an air bag deployment opening cover

ABSTRACT

A method and apparatus is disclosed for forming a cover for an air bag deployment opening, the cover having a tear seam defined by a reduction in thickness of the cover. The cover can be formed as an unitary part of an outer skin layer for an automobile interior trim structure. The apparatus includes a thin shell having an inner surface upon which a thermoplastic material is cast to form the outer skin. A multiplicity of pins are disposed on and extend away from a backside thereof to transfer heat to the inner surface. The density of the pins is reduced on the portion of the backside of the shell proximate the portion of the inner surface upon which the tear seam of the outer skin is to be formed. The shell can be heated or cooled by using a plurality of nozzles to impinge heated or cooled air onto predetermined locations of the backside. A cover and tear seam construction is also disclosed.

This is a division of application Ser. No. 07/985,916, filed on Dec. 4,1992, now U.S. Pat. No. 5,443,777.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to automotive interior trim structuresincorporating a cover for an air bag deployment opening and, inparticular, relates to a method and apparatus for casting a tear seaminto the decorative outer skin of an automobile interior trim structureby controlling the relative temperature of the portion of the mold usedto form the tear seam in the outer skin. Further, the invention relatesto a resultant cover and tear seam construction.

2. Description of the Related Art

Various types of supplemental involuntary restraint systems (SIRs) arecurrently being provided by automobile manufacturers to help reduce theextent of personal injuries incurred in automobile accidents. Air bagsare increasingly becoming one of the most common and popular SIRsutilized. Air bags are designed to inflate during a collision torestrain forward movement of the driver and/or other occupants to helpavoid injurious contact with interior portions of the automobile.Driver's side air bags currently come as standard equipment on manymodels and optional passenger side air bags are becoming more common.

Air bags are typically stowed behind one or more interior trimstructures, such as the steering wheel cover, door panel, or passengerside portion of the instrument panel. These interior trim structuresmust therefore be specially manufactured to permit deployment of the airbag upon a collision being detected. Such manufacturing entailsconsideration of a multitude of design requirements, such as thefunctional requirements of the air bag deployment system and theaesthetic requirements of the interior trim structures. Moreover, manyof these requirements involve counter-vailing considerations. Forexample, the air bag should be able to be deployed virtuallyinstantaneously upon a collision being detected. However, it should bestowed in such a manner as to 1) inhibit accidental or intentionaltampering that would interfere with its performance and 2) contribute toan overall pleasing interior appearance. In regard to the latterconsideration, it is, as a matter of human psychology, undesirable toremind the automobile occupants of the dangers of driving and theexistence of the air bag is therefore preferably made entirelyinvisible.

Interior trim structures used in automotive applications typicallycomprise a composite article having a foam layer formed between a rigidinsert and a decorative outer skin. The insert provides structuralreinforcement to the interior trim structure and is used to secure thetrim structure within the automobile interior. Because the reinforcinginsert is rigid, it either has an opening through which the air bag isdeployed or is manufactured with one or more hinges which define one ormore doors that open upon the air bag being inflated. The air bag isstowed behind this composite article until such time as it must bedeployed.

In the typical air bag deployment scheme, the air bag forces its way outof its stowed position upon expansion. Various arrangements of theinterior trim structures have been suggested to accommodate deploymentof the air bag in this manner. For example, U.S. Pat. No. 3,640,546,issued Feb. 8, 1972 to D. S. Brawn, discloses various air bagenclosures, each of which essentially comprise a pair of doors securedtogether by a seal which is ruptured upon expansion of the air bag. Theinflating air bag forces the doors to swing outwardly, thereby allowingthe air bag to expand into the automobile compartment. In one of thedisclosed embodiments, the doors are covered by an outer layer which ispreweakened along a joint line. Although this patent states that thepreweakening can be accomplished by reducing the thickness of the outerlayer along the joint line, the only means disclosed for accomplishingthat result is high frequency heating while loading.

U.S. Pat. No. 4,246,213, issued Jan. 20, 1981 to Y. Takamatsu et al.,discloses a method for casting in V-shaped cut portions that extendthrough the foam layer and partially through the outer layer to define atear seam along which the trim structure ruptures upon inflation of theair bag. The method utilizes two male mold members, each havingprojections which forms a part of the cut portion. The first mold memberis used to form the outer layer and has one or more projections whichform a groove in the back side of the outer layer. The second moldmember is used to form the foam layer and has one or more projectionsarranged to extend at their tips into the groove previously formed inthe outer layer. These projections form slits in the foam layer whichare aligned with the grooves to thereby form the V-shaped cut portions.

Arrangements utilizing a continuous foam layer and outer skin are known.For example, U.S. Pat. No. 5,082,310, issued Jan. 21, 1992 to D. J.Bauer, discloses a closure for an air bag deployment opening whichincludes a pair of rigid, hinged doors covered by a foam layer and anouter skin. The doors are connected by a bridging portion which breaksupon inflation of the air bag. The outer skin is cut (i.e., grooved)along its inside surface proximate the bridging portion of the doors todefine a tear seam along which it ruptures upon deployment of the airbag.

One problem that results from cutting or scoring a tear seam into theskin is that, at colder temperatures, the plastics used to form theouter skin become relatively brittle and the skin is therefore moresusceptible to cracking along the tear seam. At the opposite temperatureextremes, these plastics become relatively soft and deformable, therebybecoming more difficult to rupture. These offsetting considerations makeit more difficult for manufacturers to produce an outer skin having atear seam that remains unbroken when subjected to expected environmentalconditions yet will rupture when needed.

A second disadvantage of cut tear seams is that they require a separatemanufacturing step which must be completed after the outer skin isformed, but prior to co-molding the skin to the foam layer. Moreover, asshown in U.S. Pat. No. 5,082,310, discussed above, cutting the skintypically requires that it first be removed from the mold.

Another method for forming grooves in a thermoplastic material isdisclosed in U.S. Pat. No. 4,886,630, issued Dec. 12, 1989 to T. Sugiuraet al. This method, however, not only requires that the outer skinmember be preformed in a separate operation, but also requires, inaddition to the female mold member, a separate male mold member and aheated press member which extends through an aperture in the male moldmember to form the grooves.

The aforementioned shortcomings of cutting and press-forming an outerskin to form a groove therein can be avoided by casting the tear seaminto the skin during formation of the skin. Although U.S. Pat. No.4,246,213, discussed above, shows one method of casting a groove intothe tear seam, it requires a separate male mold member which must beinserted and removed from the female mold member during eachmanufacturing cycle.

Other, more suitable means of forming an outer skin are disclosed inU.S. Pat. No. 4,623,503, issued Nov. 18, 1986 to E. Anestis et al., andU.S. Pat. No. 5,032,076, issued Jul. 16, 1991 to K. L. Jackson, Jr.,each of which is hereby incorporated by reference. U.S. Pat. No.4,623,503 discloses a method and apparatus for casting an article byimpinging heated air onto the backside of a mold to fuse togethermaterial disposed on the inner surface of the mold. U.S. Pat. No.5,032,076 discloses a mold assembly having heat transfer pins located onthe outer surface of a mold shell to facilitate the transfer of heatfrom air flowing about the outer surface to the inner surface of themold.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for producing anouter skin covering for an air bag deployment opening in a automobileinterior trim structure. The cover is formed from a thermoplasticmaterial which is fused upon the surface of a mold by heating. The coverincludes a wide tear seam formed during the mold process. The method forforming the cover having such a tear seam comprises (a) placing athermoplastic material on a mold surface, (b) heating the portion of themold surface used to form the tear seam to a first temperature andsimultaneously heating the surrounding portion of the mold surface to atemperature greater than the first temperature to thereby form a layerof thermoplastic material having a thinned portion which defines thetear seam, and (c) cooling the layer of thermoplastic material.Preferably, the method includes impinging air having an elevatedtemperature onto pins extending from a back surface of the mold andtransferring heat from the air to the mold surface through the pins.

An apparatus suitable for use with this method includes a mold shellhaving an inner mold surface upon which the cover is to be formed and anouter mold surface. The shell has a multiplicity of heat transfer pinsdisposed on and extending away from the outer surface, the density ofthe pins opposite the portion of the mold surface used to form the tearseam being less than the density of the surrounding pins. The pins canbe used to form a tear seam having any desired configuration, such asthe C, H, U, and X designs commonly used in the automotive industry.Preferably, the apparatus includes a plurality of nozzles disposed toimpinge air upon the pins and outer surface of the mold shell. Thearrangement of these nozzles can be used in conjunction with the densityof the pins to balance the mold surface temperature along the portion ofthe mold surface used to form the tear seam.

The present invention simplifies production of tear seams in air bagdeployment opening covers. The tear seam is formed as a part of astandard operation for casting of the outer skin so that no secondaryoperation is needed. That is, the method and apparatus of the presentinvention provides an outer skin having a tear seam incorporated thereinwhich can be manufactured in the same amount of time that is required tomanufacture an outer skin not having a tear seam. As a result, cycletimes for manufacturing these articles is reduced and productivity istherefore increased.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the present invention willhereinafter be described in conjunction with the appended, wherein likedesignations denote like elements, and:

FIG. 1 is a perspective view of the outer surface of a mold shell of thepresent invention having heat transfer pins located thereon;

FIG. 2 is a top view of the mold shell of FIG. 1 showing in hidden linesthe portion of the inner mold surface which forms the tear seam of thepresent invention;

FIG. 3 is a partial perspective view of the mold of FIGS. 1 and 2disposed in a mold box suitable for heating and cooling the mold;

FIG. 4 is a cross-sectional view of the mold shell and mold box of FIG.3;

FIG. 5 is a perspective view of an automobile interior trim structureincorporating an invisible tear seam of the present invention made fromthe mold shell of FIG. 1;

FIG. 6 is a cross-sectional view of the interior trim structure takenalong the 6--6 line of FIG. 5;

FIG. 7 is an enlarged cross-sectional view of the structure of FIG. 6showing the details of the air bag deployment opening cover of thepresent invention;

FIG. 8 is partial perspective view of an instrument panel mounted withinan automobile interior compartment and showing in hidden lines an airbag deployment opening cover defined by a tear seam of the presentinvention; and

FIG. 9 is a partial perspective view of the instrument panel of FIG. 8with the air bag deployment opening cover having been ruptured along thetear seam.

DESCRIPTION OF PREFERRED EMBODIMENT

In accordance with a preferred embodiment, there is diagrammaticallyillustrated in FIG. 1 a mold 10 formed of a thin shell 11 having amultiplicity of heat transfer pins 12 disposed on and extending awayfrom an outer surface or backside 14 thereof. Backside 14 includes aopen portion 16 which is defined by the absence of any of the pins 12.As shown in FIG. 2, mold 10 also includes an inner surface 18 upon whicha thermoplastic material can be cast to thereby form an outer skincovering for an air bag deployment opening which is a unitary part of anautomobile interior trim structure. The contour of inner surface 18forms the exposed surface of the interior trim structure when it isplaced in its intended environment and surface 18 can therefore betextured and include other aesthetically pleasing detailing. Innersurface 18 includes a tear seam portion 20 which is defined by andlocated opposite open portion 16 of backside 14. Tear seam portion 20 isneither raised nor recessed from the surrounding portion of innersurface 18 and is therefore imperceptible when viewing inner surface 18.Accordingly, tear seam portion 20 is depicted in FIG. 2 by hidden lines.

Pins 12 facilitate the transfer of heat from air flowing about backside14 to surface 18. Therefore, the amount of heat transferred to any oneregion of surface 18 depends upon the spacing (i.e., density) of pins 12on the portion of backside 14 opposite that region. By eliminating pins12 from open portion 16, tear seam portion 20 will not achieve as hightemperatures as the surrounding portion of surface 18. As discussedbelow, utilization of this effect permits casting in a single step of alayer of thermoplastic material having a relatively thin tear seamformed upon tear seam portion 20.

The density of pins 12 along various portions of backside 14 can bevaried to provide desirable temperatures about the correspondingportions of inner surface 18. In this regard, it should become apparentto one skilled in the art that the arrangement and density of pins 12shown in the various figures are illustrative only. For instance, thepins 12 need not be completely eliminated from open portion 16, ratherthe density of pins 12 need only be reduced within portion 16 to theextent necessary to maintain the temperature of tear seam portion 20less than the temperature of the surrounding portion of inner surface 18when backside 14 is subjected to a heat source such as heated air.

Mold shell 11 preferably comprises an electro-form nickel tool which canbe constructed using known techniques. Pins 12 can be made from anythermally conductive material such as copper coated steel or nickel.Pins 12 are preferably cylindrical in shape and have an enlargeddiameter head portion at which they are attached to backside 14. Pins 12can be attached to backside 14 by capacitive discharge welding or othersuitable means and can even be formed as a unitary part of shell 11. Inparticular, pins 12 can be sized and attached to backside 14 of shell 11as described and shown in the above-mentioned U.S. Pat. No. 5,032,076,hereby incorporated by reference.

FIGS. 3 and 4 show mold 10 placed within a mold box 22 which provides aconvenient and advantageous means of heating or cooling mold 10.Backside 14 of mold 10 forms a cavity 24 with walls 26-28 of mold box22. A plurality of discharge nozzles 30 extend from wall 28. Nozzles 30each have an orifice 32 located proximate a different region of backside14. Nozzles 30 are mounted on wall 28 to permit fluidic communication tocavity 24 from a plenum 34 which is defined by interior wall 28, anouter wall 36, and side walls 38 and 40. Plenum 34 includes an inlet 42for forcing air or other fluid into plenum 34. Thus, heated or cooledair forced through inlet 42 exits plenum 34 through nozzles 30 andimpinges upon pins 12 and backside 14 to thereby heat or cool surface18, as desired. The construction and use of mold box 22 is furtherdescribed in the aforementioned U.S. Pat. No. 4,623,503, herebyincorporated by reference. Mold box 22, including nozzles 30 and plenum34, together with mold 10 comprise a mold unit 44.

OPERATION

With continuing reference to FIG. 4, a process using mold unit 44 forproducing a cover for an air bag deployment opening having a tear seamincorporated therein will hereinafter be described. Initially, mold unit44 is placed in an inverted position so that inner surface 18 facesdownwardly (e.g., as shown in FIG. 1) and mold 10 is mated with an openpowder box (not shown) containing a powdered thermoplastic material tothereby form a sealed mold chamber defined by inner surface 18 and theinterior walls of the powder box. The thermoplastic material can be adry resin powder material with suitable coloring and plasticizercontent, such as described in U.S. Pat. No. 4,923,657 issued May 8, 1990to J. C. Gembinski et al. Mold 10 is then heated to a sufficienttemperature to cause approximately one millimeter of dry powder toattach and fuse. Mold unit 44 and the powder box are then rotated 180°as a single unit to dump the dry powder against surface 18. Since innersurface 18 has been heated, a layer of the dry powder forms acrosssurface 18 and fuses together. The remaining powder is dumped back intothe powder box by rotating the powder box and mold unit 44 back to theirinitial positions. The powder box and mold unit 44 are then disconnectedand mold 10 is heated more to cure the thermoplastic material together.Finally, mold 10 is cooled to remove the layer of thermoplastic materialformed upon inner surface 18.

Automated production apparatuses for performing these steps are wellknown to those skilled in the art and more specific examples are shownin the above-mentioned U.S. Pat. No. 5,032,076, as well as U.S. Pat. No.4,610,620, issued Sep. 9, 1986 to J. D. Gray. As will be understood bythose skilled in the art, such a process could also be implemented usinga charge of liquid thermoplastic material such as liquid plastisol. Theabove-mentioned U.S. Pat. No. 4,623,503 utilizes such a process andcontains details concerning the associated apparatus for automatedimplementation of that process.

Inner surface 18 of mold 10 is heated by providing a flow of heated airalong pins 12 and backside 14. Preferably, nozzles 30 are used toprovide this air flow and can be positioned in conjunction with thedistribution of pins 12 on backside 14 to control the temperature at alllocations along inner surface 18. By selectively distributing pins 12about backside 14 and, preferably, by selectively positioning nozzles30, tear seam portion 20 of inner surface 18 can be held at a lowertemperature than the temperature of the remainder of inner surface 18when mold 10 is heated. As a result, the thickness of the layer ofthermoplastic material that fuses on inner surface 18 will be less attear seam portion 20 than at the surrounding portion.

FIGS. 5-7 show an automobile interior trim structure 50 having a coverfor an air bag deployment opening formed in accordance with the presentinvention. Structure 50 includes an outer skin layer 52, an intermediatefoam layer 54, and a rigid insert 56. Outer skin 52 has an exteriorsurface 57 which is exposed to the automobile occupants when structure50 is assembled as a component part of an automobile. Structure 50includes an air bag deployment opening defined by a pair of doors 58, 60formed as a part of insert 56 and pivotable about a pair of hinges 62,64, respectively. The portion of outer skin 52 overlying doors 58, 60comprises a cover 66 for the air bag deployment opening. Cover 66includes a tear seam portion 68 defined by a reduction in thickness ofthe surrounding main portion of the cover 66. In the illustratedembodiment, tear seam 68 comprises an H-shaped portion of cover 66. Itwill of course be understood that tear seams utilizing other shapes(e.g., C, U, or X) can be produced by arranging pins 12 on backside 14of mold shell 11 in accordance with the desired shape. Tear seam 68preferably has a width of about one half of an inch to one inch and athickness of approximately twenty to thirty thousandths of an inch. Thethickness of the portion of cover 66 surrounding tear seam 68 isapproximately forty thousandths of an inch.

Referring again briefly to FIGS. 1 and 2, those skilled in the art willunderstand that temperature gradients may exist between variouslocations on tear seam portion 20, and, accordingly, there may be aresultant variation in thickness of the layer of thermoplastic materialformed on tear seam portion 20. It is believed that the coolest regionof tear seam portion 20 will be that furthest from any of the pins 12,which, in the case of the H-shaped tear seam 68 shown in FIGS. 5- 7,would be along a line midway between the boundaries (shown as hiddenlines) of each of the three legs of H-shaped tear seam 68. This point isindicated in FIG. 7 by the arrow designated with numeral 70.

The construction of and materials used for outer skin 52, foam layer 54and insert 56 (including hinges 62, 64) are all well known to thoseskilled in the art. For example, outer skin 52 can be a polyvinylchloride or an acrylonitrile-butadiene-styrene resin.

FIG. 8 depicts structure 50 as it would be assembled as part of aninstrument panel 72 within an automobile. As indicated by the hiddenlines, tear seam 68 of cover 66 is located upon the passenger sideportion of instrument panel 72 and is invisible to the occupants. An airbag (not shown) is stowed behind cover 66 until such time as it isdeployed. Upon inflation, the air bag exerts a sufficient force on doors58, 60 of insert 56 to rupture foam layer 54 and cover 66 along tearseam 68. Doors 58, 60, pivot about hinges 62, 64 and swing outwardly,thereby forcing like portions of foam layer 54 and cover 66 to separate.The result is as shown in FIG. 9, where doors 58, 60 and cover 66 aredepicted in their open position.

It will thus be apparent that there has been provided in accordance withthe present invention a method and apparatus for forming a layer ofthermoplastic material having a tear seam formed therein which achievesthe aims and advantages specified herein. It will of course beunderstood that the foregoing description is of preferred exemplaryembodiments of the invention and that the invention is not limited tothe specific embodiments shown. For instance, in the broader aspects ofthe method of the present invention, any means of heating a portion ofinner surface 18 to a lower temperature than the surrounding portions tothereby form a layer of plastic material having a reduced thicknessalong that portion to form a tear seam for an air bag deployment openingcover can be used without departing from the scope of the presentinvention. Various changes and modifications will be apparent to thoseskilled in the art and all such variations and modifications areintended to come within the spirit and scope of the appended claims.

I claim:
 1. A thermoformed plastics cover construction for an airbagdeployment door subassembly, comprising:a main portion having a wallthickness of about 0.04 inches and a predetermined strength; and arelatively weaker tear seam portion having a predetermined geometricpattern and surrounded by said main portion, said seam portion having anas-formed seam width of about 0.5 to 1.0 inches and an as-formedmaterial thickness of about 0.02 to 0.03 inches.
 2. The coverconstruction of claim 1 wherein said geometric pattern is H-shaped.